launch_xml

XML frontend for the launch package.

README

launch_xml

This package provides an abstraction of the XML tree.

XML front-end mapping rules

Accessing xml attributes

When having an xml tag like:

<tag value="2"/>

If the entity e is wrapping it, the following statements will be true:

e.get_attr('value') == '2'
e.get_attr('value', data_type=int) == 2
e.get_attr('value', data_type=float) == 2.0

By default, the value of the attribute is returned as a string.

Allowed types are: - scalar types: str, int, float, bool - An uniform list, e.g.: List[int]. - The list of entities type: List[Entity] (see below).

List is the usual object from the typing package. data_type can also be set to None, in which case yaml rules will be used.

For handling lists, the *-sep attribute is used. e.g.:

<tag value="2,3,4" value-sep=","/>
<tag2 value="2 3 4" value-sep=" "/>
<tag3 value="2, 3, 4" value-sep=", "/>

tag.get_attr('value', data_type=List[int]) == [2, 3, 4]
tag2.get_attr('value', data_type=List[float]) == [2.0, 3.0, 4.0]
tag3.get_attr('value', data_type=List[str]) == ['2', '3', '4']

In the case a value can be either an instance of a type or a substitution, the can_be_str argument of get_attr must be used, followed by a call to parser.parse_if_substitutions:

value = e.get_attr('value2', data_type=int, can_be_str=True)
normalized_value = parser.parse_if_substitutions(value)

For checking if an attribute exists, use an optional argument:

value = e.get_attr('value', optional=True)
if value is not None:
    do_something(value)

With optional=False (default), AttributeError is raised if the specified attribute is not found.

Accessing XML children as attributes:

In this xml:

<executable cmd="ls">
    <env name="a" value="100"/>
    <env name="b" value="stuff"/>
</node>

The env children could be accessed like:

env = e.get_attr('env', data_type=List[Entity])
len(env) == 2
env[0].get_attr('name') == 'a'
env[0].get_attr('value') == '100'
env[1].get_attr('name') == 'b'
env[1].get_attr('value') == 'stuff'

In these cases, e.env is a list of entities, that can be accessed in the same abstract way.

Accessing all the XML children:

All the children can be directly accessed:

e.children

It returns a list of launch_xml.Entity wrapping each of the XML children.

Built-in substitutions

See this document.